1. Technical Field
The present invention relates to a display device such as a liquid crystal television, a light source device to be used as a light source of the display device, and a light reflection sheet for reflecting light applied from the light source of the light source device.
2. Description of Related Art
A liquid crystal display device referred to as a thin type such as a liquid crystal television includes a display unit which has, on a right side, a display surface for displaying an image and takes a shape of an almost rectangular parallelepiped, and a light source device disposed on a back side of the display unit for applying light on the display unit, and a diffusion plate and an optical sheet such as a prism sheet are provided between the light source device and the display unit.
The display unit has a liquid crystal display panel taking a shape of an almost rectangular parallelepiped. The liquid crystal display panel itself does not emit light. For this reason, an illuminating light source for displaying a video image on the display surface is required, and a backlight device is used as the illuminating light source.
As the backlight device, there are generally employed an edge light system in which a light guide is provided on a back side of a display unit and an illuminating light source is disposed on an edge side of the light guide, and a falling system in which a diffusion plate is provided on the back side of the display unit and an illuminating light source is disposed on a back side of the diffusion plate.
Referring to the edge light system of the backlight device, a cold cathode fluorescent lamp (CCFL) is provided on the edge side of the light guide and light incident from the edge of the light guide is emitted from one surface of the light guide while guiding light in the light guide. Therefore, a luminance characteristic can be enhanced in a display device including a display surface having a comparatively small area. Referring to a display device including a display surface having a comparatively large area, however, it is hard to uniformly enhance the luminance characteristic over the whole surface. For this reason, in a display device such as a television which is increasingly large-sized, the backlight device of the falling system is used.
For the backlight device of the falling system, there are generally employed, as illuminating light sources, a CCFL type in which a plurality of cold cathode fluorescent lamps (CCFLs) having electrodes on both ends and taking a shape of a straight pipe or an almost U shape are juxtaposed on a back side of the diffusion plate (for example, see Japanese Patent Application Laid-Open No. 2008-116832) and an LED type in which a plurality of light-emitting diodes (LEDs) are juxtaposed on a back side of the diffusion plate (for example, see Japanese Patent Application Laid-Open No. 2009-87879).
The backlight device of the CCFL type includes a plurality of cold cathode fluorescent lamps juxtaposed vertically apart from each other in a direction along a surface of a diffusion plate, a support case for accommodating and supporting the cold cathode fluorescent lamps, an inverter circuit board for emitting light from the cold cathode fluorescent lamps, and a cover for covering the inverter circuit board.
However, the backlight device of the CCFL type requires high voltage components such as, for example, the inverter circuit board for discharging the cold cathode fluorescent lamp, the electrodes on the both ends of the cold cathode fluorescent lamp and the like, and it is necessary to maintain a comparatively long insulating distance around the high voltage components. Therefore, the high voltage components hinder a longitudinal thickness from being reduced. For this reason, there is a tendency that a backlight device of an LED type which has no high voltage component, does not need to maintain a comparatively long insulating distance and is more advantageous to reduce a longitudinal thickness than the backlight device of the CCFL type is employed for a recent display device.
Moreover, the cold cathode fluorescent lamp is formed in a length provided over both ends in a transverse direction of the diffusion plate. For this reason, it is impossible to control a lighting operation of the cold cathode fluorescent lamp in a fine area. Furthermore, a high-speed flashing control for suppressing an animation blur or the like is more disadvantageous as compared with the LED type. In addition, power consumption is increased because the cold cathode fluorescent lamps are turned ON at a high voltage. Consequently, a heat value is also increased when the cold cathode fluorescent lamps are ON. Therefore, it is advantageous to employ the backlight device of the LED type which can easily carry out a control in a fine area and a high-speed flashing control, and furthermore, can lessen a power consumption and a heat value more greatly than the backlight device of the CCFL type.
The backlight device of the LED type includes a plurality of light-emitting diode substrates having one surface on which a plurality of light-emitting diodes are mounted, a support case for accommodating and supporting the light-emitting diode substrates, and a power board for emitting light from the light-emitting diodes.
The applicant of the present invention developed a backlight device of an LED type including a plurality of light-emitting diode substrates, each of which has a plurality of light-emitting diodes mounted on one surface and takes a shape of a strip connected in a line, a support case for accommodating and supporting the light-emitting diode substrates in a plurality of lines apart from each other in a vertical direction, a shaft member such as a rivet for fixing both ends of the light-emitting diode substrate, a connector for connecting the light-emitting diode substrates which are adjacent to each other, a plurality of lenses attached to one surface of the light-emitting diode substrate opposite to the light-emitting diode for diffusing light emitted from the light-emitting diode, a reflection sheet mounted on one of the surfaces of the light-emitting diode substrate for reflecting the light diffused by the lens, and a support pin for suppressing a flexure of the diffusion plate.
The backlight device of the LED type is assembled in accordance with the following steps (1) to (5).
(1) The support case is put flatly on a working table with an open side turned upward, and the light-emitting diode substrates which are adjacent to each other in a transverse direction are juxtaposed in a plurality of lines in the support case.
(2) The light-emitting diode substrates which are adjacent to each other are connected to each other through the connector, and a power connecting connector is connected to the end of the light-emitting diode substrate on an end side.
(3) Both ends of the light-emitting diode substrates which are juxtaposed are fixed to the support case by means of the shaft member such as a rivet.
(4) The reflection sheet is mounted on one of the surfaces of the light-emitting diode substrate.
(5) The support pins are attached to the support case from the reflection sheet side.
The support case is formed by a metal plate and has a flat plate-shaped plate portion taking a square shape, a frame portion linked to a peripheral edge of the plate portion and having one of sides opened, and four collar pieces linked to an outer edge of the frame portion. The plate portion is provided with a first mounting hole in an opposite position to the both ends of the light-emitting diode substrates which are juxtaposed, and a second mounting hole in a position in which the support pin is to be disposed.
The light-emitting diode substrate takes a shape of a strip in which a circuit portion is provided on one surface, the light-emitting diode and a lens are mounted on the surface and a connecting portion is provided on one surface of both ends, and a through hole corresponding to the first mounting hole is provided on the both ends.
The light-emitting diode is formed in such a manner that an emitted light concentrates within a predetermined angle based on an optical axis from a front of the light-emitting diode.
The lens is opposed to a top of the light-emitting diode apart from each other, and takes a shape of a thick disk having a hemispherical recess portion for diffusing light applied from the light-emitting diode in all directions.
The reflection sheet takes a square shape corresponding to the plate portion of the support case and has a structure in which a first hole taking a larger shape than the lens is provided in an opposed position to the lens and a second hole taking a larger shape than the connector is provided in an opposed position to the connector, the lens is provided in the first hole and the connector is provided in the second hole when the reflection sheet is mounted over the surface of the light-emitting diode substrate, and a thermal expansion of the reflection sheet through the light-emitting diode can be absorbed.
The light source device includes a plurality of light-emitting diode substrates having one surface on which a plurality of light-emitting diodes are mounted and juxtaposed in a plurality of lines, a support body for accommodating and supporting the light-emitting diode substrates, a light reflection sheet disposed on the light-emitting diode substrate, and a lens disposed in a portion of the light reflection sheet which is opposed to the light-emitting diode.
The light reflection sheet expands or contracts through a thermal expansion due to a rise in a temperature in the light emission of the light-emitting diode, and a warp or a flexure is caused over the light reflection sheet due to the expansion or contraction. For this reason, Patent Document 1 describes the structure in which a small diameter hole is provided on a central part of a sheet surface, a plurality of large diameter holes are provided on a peripheral edge side apart from the small diameter hole in a direction along the sheet surface, the light reflection sheet is positioned with respect to the support body with a male screw to be inserted into the small diameter hole, and the light reflection sheet is attached to the support member relatively movably through a shaft member to be loosely fitted in the large diameter hole so that the expansion or contraction caused by the thermal expansion of the light reflection sheet is absorbed by the large diameter hole.